As of November 2010, due to data from this study (P1065) and recommendations from the Advisory Committee for Immunization Practices (ACIP) of the Center for Disease Control (CDC), eligible participants in Groups 1 (1A and 1B) and 3 of P1065 received a booster dose of MCV4 at approximately 3.5 years (+/- 6 months) after the initial MCV4 vaccination. Participants were then observed for 30 minutes post-injection to monitor for adverse events. Participants were also observed at Week 1 for vaccine adverse reactions.